Gas chromatography with electron-capture detection has been used to measure total methoxyhydroxyphenyl glycol (MHPG) in human urine. Previous methods employing flame-ionization detection have proven insufficiently sensitive for our purposes. Normotensive and hypertensive subjects are under study for differences in MHPG excretion. The antihypertensive drugs clonidine, propranolol, and guanethidine are also being tested for their effects on MHPG excretion. The relationship of sodium intake and extracellular fluid volume (changed by dehydration or albumin infusion) to MHPG excretion in normal volunteers is also under evaluation. New methodology for determination of the sulfate conjugate of MHPG (believed to originate predominately in the central nervous system) via paired-ion chromatography is under development.